This invention relates generally to recirculating document feeders, and more particularly to a recirculating document feeder for use with an electrophotographic apparatus wherein a document is transported in relation to an optical path for scan exposure of such document, and having a donor/transfer member for producing simplex or duplex copies of simplex or duplex original documents.
Electrographic reproduction apparatus typically produce copies of original information on receiver members, such as cut sheets of plain bond paper for example. Such information copies may be formed on one side of the paper sheets (referred to as simplex copies), or on both sides of such sheets (referred to as duplex copies). Commercial electrographic reproduction apparatus capable of producing duplex copies are classified as "two-pass" or "single-pass" apparatus.
In "two-pass" reproduction apparatus, selected information is electrographically reproduced sequentially on the first sides of sheets respectively. Such sheets are collected in an intermediate tray and then sequentially transported from the intermediate tray back through the apparatus to have selected information respectively reproduced electrographically on the second sides of such sheets. As a result, a relatively long travel path is required for transporting sheets through the reproduction apparatus twice to produce the duplex copies. Therefore, the potential for jams or other sheet handling complications is increased. Moreover, the first completed duplex copy is not available for inspection until after all first side copies are produced. Thus considerable time elapses until the first complete duplex copy is produced, and any errors in such duplex copy are not determined until after all first side copies have already been made. Moreover, in reproducing a multi-page information document, handling of the document pages requires complex logic in that all even sides must be reproduced and collected before all odd sides are reproduced (or vice-versa).
In "single-pass" reproduction apparatus, selected information is electrographically produced respectively on both sides of a sheet during a single pass through such apparatus. While single-pass apparatus are successful in overcoming the noted disadvantages of two-pass electrographic reproduction apparatus, they tend to introduce, in and of themselves, other disadvantages or complications. For example, U.S. Pat. No. 3,775,102 (issued Nov. 27, 1973, in the name of Punnett) shows two separate substantially complete electrographic process assemblies for reproducing information respectively on each side of a sheet. Such duplicative assemblies require precise optical alignment, substantially increase apparatus cost, and add significant complexity (with reduced reliability) to the apparatus.
To eliminate duplicative process assemblies, a single-pass reproduction apparatus may employ an electrically biased donor/transfer roller for simultaneously transferring images, corresponding to information to be reproduced, respectively to each side of a receiver sheet, such as shown for example in U.S. Pat. No. 3,844,654 (issued Oct. 29, 1974, in the name of Guenther). With a doner/transfer roller, respective transferable images must be of reversed orientation (i.e. one right-reading and one wrong-reading) when initially formed so as to transfer right-reading to the receiver sheet. As shown in the arrangement of the aforementioned '654 patent, reversal of the orientation of the transferable images has been accomplished, for example, by complex optical systems with plural scanning stations and complicated document transport mechanisms. Moreover, with such arrangements direct production of simplex or duplex copies from simplex or duplex document sheets is not readily accomplished having separate optical paths and moving mirrors.